Solid curable polyene compositions containing a polythiol

ABSTRACT

Novel styrene-allyl alcohol copolymer based solid polyene compositions which when mixed with liquid polythiols can form solid curable polyene-polythiol systems. These solid polyenes, containing at least two reactive carbon-to-carbon unsaturated bonds, are urethane or ester derivatives of styrene-allyl alcohol copolymers. The solid polyenes are prepared by treating the hydroxyl groups of a styrene-allyl alcohol copolymer with a reactive unsaturated isocyanate, e.g., allyl isocyanate or a reactive unsaturated carboxylic acid, e.g., acrylic acid. Upon exposure to a free radical generator, e.g., actinic radiation, the solid polyene-polythiol compositions cure to solid, insoluble, chemically resistant, cross-linked polythioether products. Since the solid polyene-liquid polythiol composition can be cured in a solid state, such a curable system finds particular use in preparation of coatings, imaged surfaces such as photoresists, particularly solder-resistant photoresists, printing plates, etc.

This is a division, of application Ser. No. 330,818 filed Feb. 8, 1973,now U.S. Pat. No. 3,925,320 which in turn is a continuation-in-part ofSer. No. 250,554 filed May 5, 1972, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to solid styrene-allyl alcohol based polyenecompositions. More particularly, this invention relates to solid,solvent soluble curable compositions comprising solid polyenes-liquidpolythiols, method of preparing the same, as well as curing the solidpolymer compositions in the presence of a free radical generator tosolid, cross-linked, solvent-insoluble materials. More specificantly,this invention relates to solid photoresists and a method of preparingsame.

It is known that polyenes are curable by polythiols in the presence offree radical generators such as actinic radiation to solid polythioethercontaining resinous or elastomeric products. In these prior art artpolyene-polythiol curable systems, either both the polyenes andpolythiol were liquids, or one of the polymeric components was solid andthe other liquid. Both liquid curable systems and the liquid-solidcurable polymeric systems possess certain limitations and disadvantages.The use of curable liquid systems in preparation of photoimaged surfacessuch as relief printing plates and photoresists have many undesirablefeatures such as time consuming liquid coating operation which involvesthe use of cumbersome and additional apparatus, particularly expensiveliquid dispensing equipment. A particular disadvantage of the liquidpolymer systems is the resulting limited resolution during thephotoimaging step, since it is necessary to maintain an air gap betweenthe image, e.g., photographic negative and the liquid photocurablecomposition coated on a surface which is to be imaged in order to avoidmarring the image and allowing its reuse.

Additionally, in the manufacture of certain printed circuits, whenvarious photosensitive polymers are applied as liquid photoresists, theyclog "thru-holes" in double sided or multi-layer printed circuits.

On the other hand, in the prior art solid polyene-liquid polythiolcurable systems, the components are often incompatible, are not easilyworkable, or do not produce dry films, but only liquid curablecompositions.

The novel solid curable polymer system of the present inventionovercomes the numerous defects of prior art materials. The solidpolyenes of this invention which are compatible with various liquidpolythiols readily form solid curable compositions. These curablecompositions can be compounded easily by mixing the solid polyenes andthe liquid polythiols and be rapidly cured, particularly photocured in asolid state. The solid polyene-liquid polythiol mixtures are versatilephotocurable compositions which are particularly useful in preparationof solid photoresists, solid relief or offset printing plates, coatingsand the like. The subject photocurable polyene-polythiol compositionsreadily form dry solid film materials which can be easily handled andstored prior to utilizing them in photocuring processes such asphotoresist formation. The dry film polymer compositions can be readilylaminated on a desired solid surface such as photoresist formation,selective portions of the solid photocurable polymer composition arephotocured and insolubilized, thereby forming a protective coating whichshows excellent adhesion to metal surfaces such as copper.

In accordance with this invention, a solid curable polyene containing atleast 2 reactive carbon to carbon bonds per molecule can be readilyprepared from styrene-allyl alcohol copolymer starting materials. Thesestyrene-allyl alcohol copolymer based polyenes, when admixed with liquidpolythiols, form highly reactive compositions which are capable of beingphotocured when exposed to actinic radiation in the presence of a UVsensitizer to insoluble polythioether containing materials which exhibitexcellent physical and chemical properties. For example, photoresistcoatings formed from cured polyene-polythiol compositions containingstyrene-allyl alcohol copolymer based solid polyenes and liquidpolythiols are capable of withstanding severe chemical environmentsemployed in the printed circuit board manufacturing processes. Thesubject cured materials resist strongly acid etching solutions or highlyalkaline conditions of electroless metal plating baths. The desirablecharacteristics of the cured materials make the polyene-polythiolcurable compositions containing styrene-allyl alcohol copolymer backbonebased solid polyene particularly useful in both subtractive and additivecircuitry applications.

Generally speaking, the novel solid curable composition is comprised ofa solid polyene component containing at least 2 reactive carbon tocarbon unsaturated bonds per molecule which is a reaction product of acopolymer of styrene-allyl alcohol and at least one unsaturated organiccompound such as ene-acid or ene-isocyanate; and a liquid polythiolcomponent containing at least two thiol groups.

The formation of such solid polyenes may be schematically represented bythe following non-limiting equation, wherein the unsaturated organiccompound reactant is an ene-isocyanate having reactive allylic endgroups as illustrated by a reaction product of one mole of 2,4-toluenediisocyanate with one mole of allyl alcohol: ##STR1## In the aboveequation, z is at least 2.

It is be noted that in the above equation no attempt to show structuralarrangement of the polymer is to be inferred.

Broadly, the operable polyene components of the solid curablecomposition are solid derivatives of styrene-allyl alcohol copolymers inwhich the reacting group is the hydroxyl functionality of the allylalcohol portion of the copolymer. Operable solid polyenes include butare not limited to unsaturated ester and urethane derivatives ofstyrene-allyl alcohol copolymers.

As used herein, styrene-allyl alcohol copolymers refer to copolymers ofan ethylenically unsaturated alcohol and a styrene monomer. Operablestyrene-allyl alcohol copolymers are those containing from about 30 to94 percent by weight of the styrene monomer, and preferably 60 to 85percent by weight and correspondingly, from about 70 to 6 percent byweight of the ethylenically unsaturated alcohol, and preferably fromabout 40 to 15 percent on the same basis. In general, styrene-allylalcohol copolymers having from about 1.8 to 10 percent hydroxyl groupsby weight, preferably 4 to 8 percent.

The actual hydroxyl group content of the aforesaid copolymers may notalways conform to the theoretical content calculated from the relativeproportions of styrene monomer and ethylenically unsaturated alcohol,due to possible destruction of hydroxyl groups during copolymerization.

The styrene monomer moiety of said copolymer may be styrene or aring-substituted styrene in which the substituents are 1-4 carbon atomalkyl groups or chlorine atoms. Examples of such ring-substitutedstyrenes include the ortho, meta- and para-, methyl, ethyl, butyl, etc.monalkyl styrenes; 2,3- 2,4-dimethyl and diethyl styrenes; mono-, di-and tri-chlorostyrenes; alkylchlorostyrenes such as2-methyl-4-chlorostyrene, etc. Mixtures of two or more of such styrenemonomer moieties may be present. The ethylenically unsaturated alcoholmoiety may be allyl alcohol, methallyl alcohol, or a mixture thereof.For the purposes of brevity and simplicity of discussion, the entireclass of copolymers set forth in this paragraph shall hereinafter bereferred to simply as styrene-allyl alcohol copolymers.

The styrene-allyl alcohol copolymers may be prepared in several ways.One operable method which yields styrene-allyl copolymer startingmaterials which are solid products is taught in U.S. Pat. No. 2,630,430.A more desirable method of copolymerizing the styrene and allyl alcoholcomponents in a substantially oxygen-free composition, thus minimizingthe oxidative loss of hydroxyl groups, is disclosed in U.S. Pat. No.2,894,938.

Furthermore, the suitable styrene-allyl alcohol copolymers are generallycommercially available materials.

The aforedescribed styrene-allyl alcohol copolymers are operablestarting materials for the formation of the solid polyenes.

The polyenes of the subject invention have a molecular weight in therange of 332 to 20,000, preferably from 1200 to 10,000.

One group of operable polyenes containing styrene-allyl alcoholcopolymer backbones are unsaturated urethane derivatives. These solidpolyenes, i.e., unsaturated urethane derivatives of styrene-allylalcohol copolymers may be represented by the general formula: ##STR2##wherein Q is a styrene-allyl alcohol copolymeric moiety remaining aftern hydroxy groups of a said styrene-allyl alcohol copolymer, have reactedto form n urethane, i.e., ##STR3## linkages; A and B are polyvalentorganic radical members free of reactive carbon to carbon unsaturationand containing group members such as aryl, substituted aryl, aralkyl,substituted aralkyl, cycloalkyl, substituted cycloalkyl, alkyl andsubstituted alkyl containing 1 to 36 carbon atoms and mixtures thereof.These group members can be internally connected to one another by achemically compatible linkage such as --O--, --S--, carboxylate,carbonate, carbonyl, urethane and substituted urethane, urea andsubstituted urea, amide and substituted amide, amine and substitutedamine and hydrocarbon. Z is a divalent chemically compatible linkagesuch as ##STR4## --O-- and --S--, preferably ##STR5##

Preferred examples of operable aryl members are either phenyl ornapthyl, and of operable cycloalkyl members which have from 3 to 8carbon atoms. Likewise, preferred substituents on the substitutedmembers may be such groups as chloro, bromo, nitro, acetoxy, acetamido,phenyl, benzyl, alkyl and alkoxy of 1 to 9 carbon atoms, and cycloalkylof 3 to 8 carbon atoms.

X is a member selected from the group consisting of:

a. --(CH₂)_(d) --CR'=CHR

b. --O(CH₂)_(d) --CR'=CHR

c. --S--(CH₂)_(d) --CR'=CHR

d. --(CH₂)_(d) --C.tbd.CR

e. --O--(CH₂)_(d) --C.tbd.CR

f. --S--(CH₂)_(d) --C.tbd.CR

and mixtures thereof; and R and R' each are independently either ahydrogen or methyl radical, preferably a hydrogen radical; and d, p andq each are integers from 0 to 1; y is an integer from 1 to 10,preferably 1 to 5; m is an integer of at least 1, preferably from 1 to4, and more particularly from 1 to 2, and n is an integer of at least 1,and preferably 2 or greater, and more particularly from about 4 to 10,with the proviso that when n is 1, y or m is at least 2.

As used herein, polyenes and polyynes refer to simple or complex speciesof alkenes or alkynes having a multiplicity of pendant or terminallyreactive carbon to carbon unsaturated functional groups per averagemolecule. For example, a diene is a polyene that has two reactive carbonto carbon double bonds per average molecule, while a diyne is a polyynethat contains two reactive carbon to carbon triple bonds per averagemolecule; a solid polyene which is a reaction product of a styrene-allylalcohol copolymer having about 8 hydroxyl groups per average moleculeand a reactive unsaturated monoisocyanate having one terminal reactivecarbon to carbon double bond per average molecule is a complex polyenewhich contains in its structure 8 reactive carbon to carbon double bondsper average molecule. For purposes of brevity, all these classes ofcompounds will be referred to hereafter as polyenes.

In defining the position of the reactive functional carbon to carbonunsaturation, the term terminal is intended to mean that functionalunsaturation is at an end of the main chain in the molecule. The termpendant means that the reactive carbon to carbon unsaturation is locatedterminal in a branch of the main chain as contrasted to a position at ornear the ends of the main chain. For purposes of brevity, all of thesepositions are referred to herein generally as terminal unsaturation.

Functionality as used herein refers to the average number of end orthiol groups per molecule in the polyene or polythiol, respectively. Forexample, a triene is a polyene with an average of three reactive carbonto carbon unsaturated groups per molecule, and thus has a functionality(f) of three. A dithiol is a polythiol with an average of two thiolgroups per molecule and thus has a functionality (f) of two.

The term reactive unsaturated carbon to carbon groups means groups whichwill react under proper conditions as set forth herein with thiol groupsto yield the thioether linkage ##STR6## as contrasted to the termunreactive carbon to carbon unsaturation which means ##STR7## groupsfound in aromatic nuclei (cyclic structures exemplified by benzene,pyridine, anthracene, and the like) which do not under the sameconditions react with thiols to give thioether linkages. For purposes ofbrevity, this term will hereinafter be referred to generally as reactiveunsaturation or a reactive unsaturated compound.

As used herein, the term polyvalent means having a valence of two orgreater.

A general method of forming the urethane containing styrene-allylalcohol copolymer based polyene is to react the styrene-allyl alcoholcopolymer represented by a general formula Q-(OH)_(n), in which n is atleast 1 and Q is as hereinbefore set forth; with at least one reactiveunsaturated isocyanate of the general formula NCO-A--Z_(p) -B_(q)-(X)_(y) ]_(m) in which the members A, Z, B, X and the integers p, q, yand m are as hereinbefore set forth.

The term reactive unsaturated isocyanate will hereinafter be referred toas an ene-isocyanate or an yne-isocyanate.

The reaction is carried out in a moisture free atmosphere at atmosphericpressure at a temperature in the range from about 30° to 100° C.,preferably from about 40° to 80° C., for a period of about 10 minutes toabout 24 hours. The reaction is preferably a one step reaction whereinall the reactants are charged together. The ene-isocyanate oryne-isocyanate is added in a stoichiometric amount necessary to reactwith the hydroxy groups in the styrene-allyl alcohol copolymer. Thereaction, if desired, may be carried out in the presence of a catalystand inert solvent. Operable non-limiting catalysts include tin catalystssuch as dibutyl tin dilaurate, stannous octoate; tertiary amines such astriethylene diamine or N,N,N',N'-tetramethyl-1,3-butanediamine, etc.Useful inert solvents include aromatic hydrocarbons, halogenatedsaturated aliphatic or aromatic hydrocarbons and mixtures thereof.Representative non-limiting examples include benzene, chlorobenzene,chloroform, 1,1,1-trichloroethane, 1,2-dichloroethane and the like.

Operable ene- or yne- isocyanates having the above defined generalformula include, but are not limited to, simple monoene-isocyanates suchas allyl isocyanate, 2-methallyl isocyanate, crotyl isocyante, etc.

The aforementioned reactive unsaturated isocyanates are a group ofcompounds having the above general formula of operable ene- oryne-isocyanates wherein the integers p and q are 0 and m is 1. Thus, theurethane styrene-allyl alcohol copolymer based polyenes formed for thesereactive unsaturated isocyanates may be represented by simplifying thegeneral formula for the polyenes to the following specific formula:##STR8## wherein preferably y is 1 and n is 2 and the other membersbeing as hereinbefore set forth.

Other operable ene- or yne-isocyanates are those prepared by reacting apolyisocyanate of the general formula A--NCO)_(x), in which x is atleast 2 and A is as hereinbefore set forth; with a reactive unsaturatedalcohol of the general formula [(X)_(y) -B--OH in which B, X and y areas hereinbefore set forth.

The above polyisocyanate and alcohol reactants are added in suchstoichiometric amounts that x-1 isocyanate groups react go give x-1urethane linkages.

Operable non-limiting examples of starting polyisocyanate reactantsinclude hexamethylenediisocyanate, tolylene diisocyanate, xylylenediisocyanate, methylenebis (phenyl isocyanate), 4,4'-methylene(cyclohexyl isocyanate), 1-methoxy-2,4,6-benzenetrisocyanate,2,4,4'-triisocyanatodiphenylether, diphenylmethane tetraisocyanates,polyisocyanates having various functional groups such asN,N',N"-tris(isocyanatohexyl)-biuret or adducts or polyalcohols anddiisocyanates which have at least 2 free isocyanate groups. Adduct oftrimethylolpropane and 3 moles of toluene diisocyanate, is suitable.

Illustrative of the operable reactive unsaturated alcohols which mayreact with the polyisocyanates to give the desired eneisocyanate includebut are not limited to allyl and methallyl alcohol, crotyl alcohol,ω-undecylenyl alcohol, 2-vinyloxyethanol, vinylhydroxyethyl sulfide,propargyl alcohol, 1-allylcyclopentanol, 2-methyl-3-butene-2-ol.Reactive unsaturated derivatives of polyhydric alcohols such as glycols,triols, tetraols, etc., are also suitable. Representative examplesinclude trimethylolpropane or trimethylolethane diallyl ethers,pentaerythritol triallyl ether and the like. Mixtures of variousreactive unsaturated alcohols are operable as well. A suitableene-isocyanate prepared by treating one mole of trimethylbenzenetriisocyanate with two moles of trimethylolpropane diallyl ether. Theresulting urethane containing ene-isocyanate is a polyene having fourreactive allyl ether groups per molecule. Mixtures of various ene- oryne-isocyanates are operable as well.

Another class of solid polyenes operable in forming the solid curablepolyene-polythiol system of the subject invention are esters ofstyrene-allyl alcohol copolymers. Similarly, these polyenes may berepresented by the general formula ##STR9## wherein Q is a styrene-allylalcohol copolymeric moiety remaining after removal of n hydroxyl groupsfrom a said styrene-allyl alcohol copolymer thereby forming an esterlinkage; the members A, B, and X and integers p, q, y, n and m are ashereinbefore set forth in the urethane containing styrene allyl-alcoholcopolymer based polyene and k is an integer from 0 to 1.

A general method of forming these esters is to react the styrene-allylalcohol copolymer represented by the aforedefined general formulaQ--OH)_(n) ; with at least one reactive unsaturated monocarboxylic acidof the general formula: ##STR10## in which the members A, B and X, andthe integers k, p, q, y and n are as hereinbefore set forth. The termreactive unsaturated carboxylic acid will hereinafter be referred to asan ene- and/or an yne-acid.

The esterification reaction may be carried out in a conventional mannerin the presence of an acid catalyst, the water formed during thereaction being removed as an azeotrope.

Operable ene- or yne-acids include but are not limited to simplemonoene-acids such as acrylic acid, methacrylic acid, vinylacetic acid,5-hexenoic acid, 6-heptynoic acid, propiolic acid and the like.

These aforementioned reactive unsaturated acids are a group of acidshaving the above general formula of operable ene- or yne-acids whereinthe integers p and q are 0, and m is 1. Thus the ester containingstyrene-allyl alcohol copolymer based polyenes formed from thesereactive unsaturated acids may be represented by simplifying the generalformula for the polyenes to the following specific formula: ##STR11##wherein, preferably, y is 1 and n is 2 and the other members being ashereinbefore set forth.

Other operable acids are those containing more than one terminallyreactive unsaturated group in the molecule. These may be prepared byreacting a polycarboxylic acid of the general formula A-(COOH)_(x), inwhich x is at least 2 and A is as hereinbefore set forth, with areactive unsaturated alcohol of the general formula [(X)_(y) -B]-OH, inwhich B, X and y are as hereinbefore set forth.

The above polycarboxylic acid and alcohol reactants are added in suchstoichiometric amounts that x-1 carboxylic groups react to give x-1ester linkages.

Operable polycarboxylic acids include but are not limited todicarboxylic acids such as adipic, tartaric, succinic, terephthalic,etc.

Operable reactive unsaturated alcohol components are the same asdescribed above as being suitable in forming ene-isocyanates. As anexample, a suitable ene-acid can be prepared by reacting one mole oftrimethylolpropane diallyl ether with one mole of succinic anhydride inthe presence of pyridine as a solvent. The resulting succinate productcontains a free carboxylic group as well as two reactive allyl ethergroups.

The liquid polythiols used herein for curing to a 3 dimensional networkare simple or complex organic compounds having a multiplicity of pendantor terminally positioned --SH functional groups per average molecule.

On the average the liquid polythiol used for curing must contain 2 ormore --SH groups/molecule and have a viscosity range of slightly above 0to 20 million centipoises (cps) at 25° C as measured by a BrookfieldViscometer. Operable polythiols used for curing in the instant inventionusually have molecular weights in the range about 94 to about 20,000,and preferably from about 100 to about 10,000.

The liquid polythiols used for curing in the instant invention may beexemplified by the general formula R₈ --SH)_(x) where x is at least 2and R₈ is a polyvalent organic radical member free from reactivecarbon-to-carbon unsaturation. Thus R₈ may contain cyclic groupings andminor amounts of hetero atoms such as N, P or O but primarily containscarbon-carbon, carbon-hydrogen, carbon-oxygen, or silicon-oxygencontaining chain linkages free of any reactive carbon-to-carbonunsaturation.

Certain polythiols such as the aliphatic monomeric polythiols (ethanedithiol, hexamethylene dithiol, decamethylene dithiol,tolylene-2,4-dithiol, and the like, and some polymeric polythiols suchas a thiol-terminated ethylcyclohexyl dimercaptan polymer, and the like,and similar polythiols which are conveniently and ordinarily synthesizedon a commercial basis, although having obnoxious odors, are operable butmany of the end products are not widely accepted from a practical,commercial point of view.

One class of liquid polythiols operable with polyenes to obtainessentially odorless polythioether products are liquid esters ofthiol-containing acids of the formula HS--R₉ --COOH where R₉ is apolyvalent organic radical member containing no reactivecarbon-to-carbon unsaturation with polyhydroxy compounds of structureR₁₀ --OH)_(x) where R₁₀ is a polyvalent organic radical membercontaining no reactive carbon to carbon unsaturation, and x is 2 orgreater. These components will react under suitable conditions to give apolythiol having the general structure: ##STR12## where R₉ and R₁₀ arepolyvalent organic radical members containing no reactivecarbon-to-carbon unsaturation, and x is 2 or greater.

In the above formula for the polythiol ester R₁₀ is a radical memberremaining after removal of x hydroxyl groups from a polyhydric alcohol.R₉ is a polyvalent, particularly divalent organic radical memberselected from the group consisting of aryl, substituted aryl, aralkyl,substituted aralkyl, cycloalkyl, substituted cycloalkyl, alkyl andsubstituted alkyl groups containing 1 to 16 carbon atoms.

Preferred examples of operable aryl members are either phenyl or benzyl,and of operable cyloalkyl members which have from 3 to 8 carbon atoms.Likewise, preferred substituents on said substituted members selectedfrom the group consisting of nitro, chloro, bromo, acetoxy, acetamido,phenyl, benzyl, alkyl, and alkoxy and cycloalkyl; said alkyl and alkoxyhaving 1 to 9 carbon atoms and cycloalkyl of 3 to 8 carbon atoms.

Operable polyhydroxy compounds are polyhydric alcohols such as variousglycols, triols, tetraols, pentaols, hexaols and the like. Non-limitingexamples of polyhydric alcohols include simple aliphatic orcycloaliphatic polyols such as ethylene glycol 1,3 butanediol,trimethylolethane, 1,4-cyclohexanediol as well as halogenatedderivatives such as 2-chloro-1,3-propanediol,2,3-dichloro-1,4-butanedioland the like.

Additional operable polyhydroxy compounds are glycols formed from poly(alkylene oxides) such as polyethylene glycols, polypropylene glycols,polybutylene glycols or mixed poly(alkylene oxide) glycols. Preferably,the molecular weight of these polyols is within the range of 300 to25,000 and especially within the range of 1500 to 6000.

Other suitable polyhydric alcohols containing oxygen atoms in the mainchain are those formed by addition of an alkylene oxide, especiallyethylene or propylene oxide to a triol or higher polyol. A specificexample of a preferred polyol is an ethoxylated pentaerythritol.

Operable mercaptocarboxylic acids include but are not limited tothioglycollic acid (mercaptoacetic acid), α-mercaptopropionic acid,β-mercaptopropionic acid, 4-mercaptobutyric acid, mercaptoundecyclicacid, mercaptostearic acid, and o-and p-mercaptobenzoic acids.Preferably, α or β -mercaptopropionic acid or thioglycollic acids areemployed, since polythiol esters derived from these acids generallypossess relatively low odor level and are compatible with the subjectsolid polyenes.

Specific examples of the preferred polythiols include but are notlimited to ethylene glycol bis (thioglycolate), ethylene glycol bis(β-mercaptopropionate), trimethylolpropane tris (thioglycolate),trimethylolpropane tris (β-mercaptopropionate), pentaerythritol tetrakis(thioglycolate) and pentaerythritol tetrakis (β-mercaptopropionate), allof which are commercially available. A specific example of a preferredpolymeric polythiol is polypropylene ether glycol bis(β-mercaptopropionate) which is prepared from polypropylene-ether glycol(e.g. Pluracol 2010, Wyandotte Chemical Corp.) and β-mercaptopropionicacid by esterification.

The preferred polythiol compounds are characterized by a low level ofmercaptan-like odor initially, compatibility with the solid polyenes andafter reaction, give essentially odorless polythioether end productswhich are commercially attractive and practically useful solid curedpolymeric materials for both indoor and outdoor applications.

The polythiol esters may be prepared in a conventional manner, e.g., byreaction of the polyhydric alcohol component with the mercaptocarboxylicacid in the presence of an acid catalyst, the water formed during thereaction being removed as an azeotrope with a suitable solvent.

In summary, by admixing the novel solid styrene-allyl alcohol copolymerbased polyenes with various liquid polythiols and thereafter exposingthe solid mixture at ambient conditions to a free radical generator, asolid, cured insoluble polythioether product is obtained.

Prior to curing the solid polyene and liquid polythiol, components areadmixed in a suitable manner so as to form a homogenous solid curablemixture. Thus, the polyene and polythiol reactants may be dissolved in asuitable solvent and thereafter the solvent can be removed by suitablemeans such as evaporation.

To obtain the maximum strength, solvent resistance, creep resistance,heat resistance and freedom from tackiness, the reactive componentsconsisting of the polyenes and polythiols are formulated in such amanner as to give solid, crosslinked, three dimensional networkpolythioether polymer systems on curing. In order to achieve suchinfinite network formation, the individual polyenes and polythiols musteach have a functionality of at least 2 and the sum of thefunctionalities of the polyene and polythiol components must always begreater than 4. Blends and mixtures of various solid polyenes andvarious liquid polythiols containing said functionality are alsooperable herein.

The solid compositions to be cured in accord with the present inventionmay, if desired, include such additives as antioxidants, accelerators,dyes, inhibitors, activators, fillers, thickeners, pigments, anti-staticagents, flame-retardant agents, surface-active agents, extending oils,plasticizers and the like within the scope of this invention. Suchadditives are usually pre-blended with the polyene or polythiol prior toor during the compounding step. The aforesaid additives may be presentin quantities up to 500 or more parts based on 100 parts by weight ofthe polyene-polythiol curable compositions and preferably 0.005-300parts on the same basis.

The solid polythioether-forming components and compositions, prior tocuring may be admixed with or blended with other monomeric and polymericmaterials such as thermoplastic resins, elastomers or thermosettingresin monomeric or polymeric compositions. The resulting blend may besubjected to conditions for curing or co-curing of the variouscomponents of the blend to give cured products having unusual physicalproperties.

Although the mechanism of the curing reaction is not completelyunderstood, it appears most likely that the curing reaction may beinitiated by most any free radical generating source which dissociatesor abstracts a hydrogen atom from an SH group, or accomplishes theequivalent thereof. Generally, the rate of the curing reaction may beincreased by increasing the temperature of the composition at the timeof initiation of cure. In many applications, however, the curing isaccomplished conveniently and economically by operating at ordinary roomtemperature conditions.

Operable curing initiators or accelerators include radiation such asactinic radiation, e.g., untraviolet light, lasers; ionizing radiationsuch as gamma radiation, X-rays, corona discharge, etc.; as well aschemical free radical generating compounds such as azo, peroxidic, etc.,compounds.

Azo or peroxidic compounds (with or without amine accelerators) whichdecompose at ambient conditions are operable as free radical generatingagents capable of accelerating the curing reaction include benzoylperoxide, di-t-butyl peroxide, cyclohexanone peroxide with dimethylaniline or cobalt naphthenate as an accelerator; hydroperoxides such ashydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxides; peracidcompounds such as t-butylperbenzoate, peracetic acid; persulfates, e.g.,ammonium persulfate; azo compounds such as azobis-isobutyronitrile andthe like.

These free radical generating agents are usually added in amountsranging from about 0.001 to 10 percent by weight of the curable solidpolyene-polythiol composition, preferably 0.01 to 5 percent.

The curing period may be retarded or accelerated from less than 1 minuteto 30 days or more.

Conventional curing inhibitors or retarders which may be used in orderto stabilize the components or curable compositions so as to preventpremature onset of curing may include hydroquinone; p-tert-butylcatechol; 2,6-di tert-butyl-p-methylphenol; phenothiazine;N-phenyl-2-naphthylamine; phosphorous acid; pyrogallol and the like.

The preferred free radical generator for the curing reaction is actinicradiation, suitably in the wavelength of about 2000 to 7500A, preferablyfor 2000 to 4000A.

A class of actinic light useful herein is ultraviolet light, and otherforms of actinic radiation which are normally found in radiation emittedfrom the sun or from artificial sources such as Type RS Sunlamps, carbonarc lamps, xenon arc lamps, mercury vapor lamps, tungsten halide lampsand the like. Ultraviolet radiation may be used most efficiently if thephotocurable polyene/polythiol composition contains a suitablephotocuring rate accelerator. Curing periods may be adjusted to be veryshort and hence commercially economical by proper choice of ultravioletsource, photocuring rate accelerator and concentration thereof,temperature and molecular weight, and reactive group functionality ofthe polyene and polythiol. Curing periods of less than about 1 secondduration are possible, especially in thin film applications such asdesired, for example, in coatings, adhesives and photoimaged surfaces.

Various photosensitizers, i.e., photocuring rate accelerators areoperable and well known to those skilled in the art. Examples ofphotosensitizers include, but are not limited to, benzophenoneo-methoxybenzophenone, acetophenone, o-methoxyacetophenone,acenaphthene-quinone, methyl ethyhl ketone, valerophenone,hexanophenone, α-phenylbutyrophenone, p-morpholinopropiophenone,dibenzosuberone, 4-morpholinobenzophenone, benzoin, benzoin methylether, 4'-morpholinodeoxybenzoin, p-diacetylbenzene,4-aminobenzophenone, 4'-methoxyacetophenone, benzaldehyde,o-methoxybenzaldehyde, α-tetralone, 9-acetylphenanthrene,2-acetylphenanthrene, 10-thioxanthenone, 3-acetylphenanthrene,3-acetylindole, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene,thioxanthen-9-one, xanthene-9-lone, 7-H-benz[de]anthracen-7-one,1-naphthaldehyde, 4,4'-bis(dimethylamino)benzophenone, fluorene-9-one,1'acetonaphthone, 2'-acetonaphthone, triphenylphosphine,tri-o-tolylphosphine, acetonaphthone and 2,3-butanedione,benz[a]anthracene 7,12 dione, etc., which serve to give greatly reducedexposure times and thereby when used in conjunction with various formsof energetic radiation yield very rapid, commercially practical timecycles by the practice of the instant invention.

These photocuring rate accelerators may range from about 0.005 to 50percent by weight of the solid photocurable polyenepolythiolcomposition, preferably 0.05 to 25 percent.

The mole ratio of the ene/thiol groups for preparing the solid curablecomposition is from about 0.2/1.0 to about 8/1.0, and preferably from0.5/1.0 to about 2/1.0 group ratio.

The solid curable polyene-polythiol compositions containingstyrene-allyl alcohol copolymer based solid polyenes are used inpreparing solid, cured cross-linked insoluble polythioether polymericproducts having many and varied uses, examples of which include, but arenot limited to, coatings; adhesives; films; molded articles; imagedsurfaces, e.g., solid photoresists; solid printing plates; e.g., offset,lithographic, letterpress, gravures, etc., silverless photographicmaterials and the like.

Since the cured materials formed from the solid polyeneliquid polythiolcompositions possess various desirable properties such as resistance tosevere chemical and physical environments, they are particularly usefulfor preparing imaged surfaces.

A general method for preparing coatings, particularly imaged surfacessuch as photoresists, printing plates, etc., comprises coating the solidcurable composition on a solid surface of a substrate such as plastic,rubber, glass, ceramic, metal, paper and the like; exposing image-wiseeither directly using "point" radiation or through an image bearingtransparency, e.g., photographic negative or positive or a mask, e.g.,stencil, to radiation, e.g., U.V. light until the curable compositioncures and cross-links in the exposed areas. After image-wise exposure,the uncured, unexposed areas are removed, e.g., with an appropriatesolvent, thereby baring the unprotected surface of the substrate inselected areas. The resulting products are cured latent images onsuitable substrates or supports. In case or preparing printing plates,e.g., a flexible relief plate wherein the substrate is usually a plasticmaterial, the imaged product is ready for use. However, in other cases,e.g., in printed circuit manufacture or in chemical milling, the curedpolymer composition acts as a photoresist.

The solid curable polyene-polythiol compositions of the subjectinvention are extremely suitable for use as a photoresist compositionsince (1) it adheres to the substrate firmly and readily on photocuring,(2) is resistant to the etching and plating environments for thesubstrate as well as soldering environments and (3) is easily removed bya solvent which does not affect the protected area.

Thus, in the preparation of an imaged surface by one operablephotoresist process, the solid photocurable polyenepolythiol compositionis coated or laminated onto an etchable solid surface, preferably ametal or metal clad substrate, as a solid, tack-free layer; exposedthrough an image bearing transparency to a free radical generator suchas actinic radiation suitably in the wavelength range from about 2000 to7500A or ionizing radiation to selectively cure the exposed portion ofthe composition, thus baring the metal beneath the removed uncuredportion of the composition, optionally removing the exposed metal fromthe substrate to the desired depth and thereafter optionally removingthe cured composition, thus leaving defined metal areas on thesubstrate.

In the printed circuit board manufacturing processes, the solid surfaceor board is usually electrically insulating substrate such as ceramic,thick plastic, epoxy, glass, etc., which can be clad with an etchablemetal such as copper, aluminum, nickel, stainless steel and the like.

The above process illustrates the use of the solid photoresist insubstractive circuitry applications, however, the subject solidphotoresist compositions are very satisfactory for use in additivecircuitry applications which utilize electroless metal plating processeswhich generally have highly caustic plating baths and thus require anextremely resistant photoresist material. Typical electroless metalplating baths, as well as conventional sensitizing and activatingsolutions utilized in additive circuit processes are disclosed in U. S.Pat. Nos. 3,546,009 and 3,573,973.

Various metals such as copper, nickel, gold, silver, tin, lead, etc.,may be plated on metal clad substrates by conventional metal depositingtechniques other than electroless plating, such as electroplating,chemical vapor deposition, flow soldering coating techniques and thelike. The subject photocured resist composition are capable ofwithstanding the various metal depositing environments.

The solid film of photocurable composition can be formed by coating asolution or dispersion onto the metal cladding of a substrate and dryingthe layer by removal of the solvent by any suitable means, such asevaporation. The solid photoresist compositions may also be melted andsuitably applied directly onto the metal surface of a metal cladsubstrate. Coating may be carried out by any of the conventional coatingprocedures such as spraying, dip coating, roller coating or curtaincoating.

The photocurable resist layer has usually a dry coating thickness ofabout 1 mil, although it may range from 0.015 to about 5 mils or more,e.g., layers up to 10 mils are satisfactory.

In forming the solid photoresist composition comprised of the solidpolyene and liquid polythiol, it is desirable that the photocurablecomposition contain a photocuring rate accelerator

from about 0.005 to 50 parts by weight based on 100 parts by weight ofthe aforementioned polyene and polythiol.

It is to be understood, however, that when energy sources, e.g.,ionizing radiation, other than visible or ultraviolet light, are used toinitiate the curing reaction, photocuring rate accelerators (i.e.,photosensitizers, etc.) generally are not required in the formulation.

When U.V. radiation is used for the curing reaction, a dose of 0.0004 to6.0 watts/cm² is usually employed.

The thickness of the metal or metal cladding on the substrates may varyfrom 0.1 mil to 20 mils, depending on the desired end use.

The following examples will aid in explaining, but should not be deemedlimiting, the instant invention. In all cases unless otherwise noted,all parts and percentages are by weight.

PREPARATION OF SOLID POLYENES EXAMPLE 1

In a 1-liter flask maintained under a nitrogen atmosphere and equippedwith a stirrer, thermometer, condenser and a gas inlet and outlet, wasadded 348 g (2.0 moles) of toluene diisocyanate (a 80/20 mixture of the2,4 and 2,6 isomers). 116 g (2.0 moles) of allyl alcohol was slowlyadded over a period of 2 hours to the reaction vessel with stirringduring which time the exotherm and reaction temperature wre maintainedbelow about 70° C. After the addition of the allyl alcohol was completedthe reaction was continued for about 15 hours at about 25° C. The thusformed liquid monoallyl urethane had an NCO content of 4.13 meq/g and anunsaturation of 4.5 mmoles/g. This product will hereinafter be referredto as ene-isocyanate A.

EXAMPLE 2

110 g of a copolymer of styrene allyl alcohol having an equivalentweight of about 220 and a hydroxyl content of about 7.7 percent andcommercially available from Monsanto Company under the tradename RJ 101,was dissolved in 300 ml of benzene in a 1-liter reaction flaskmaintained under a nitrogen atmosphere and equipped with a stirrer,condenser, thermometer and a gas inlet and outlet. 0.6 g of dibutyltindilaurate as a catalyst was added to the reaction flask followed bydropwise addition over a period of 1/2 hour of 116 g of theene-isocyanate A prepared in Example 1. The reaction was allowed tocontinue for about 15 hours while maintaining the temperature at about70° C. Thereafter, the reaction mixture was cooled to room temperatureand the solvent was removed under vacuum. The resulting solid polyenehaving a styrene-allyl alcohol based polymeric backbone (190 g) had anunsaturation of 2.2 mmoles/g and a melting point of 85°-105° C. Thispolyene will hereinafter be referred to as Polyene A.

EXAMPLE 3

Example 2 was repeated except that 150 g of a copolymer of styrene-allylalcohol having an equivalent weight of about 300 and a hydroxyl contentof about 5.7 percent and commercially available from Monsanto Companyunder the tradename RJ 100, instead of the RJ 101 was employed as thestyrene-allyl alcohol copolymer backbone and the benzene solvent wasreplaced by 1,2-dichloroethane. The resulting solid was an allylterminated polyene having a styrene-allyl alcohol copolymer basedpolymeric backbone. This polyene will hereinafter be referred to asPolyene B.

EXAMPLE 4

220 g of a copolymer of styrene allyl-alcohol having an equivalentweight of about 220 and a hydroxyl content of about 7.7 percent andcommercially available from Monsanto Company under the tradename RJ 101,and 72.0 g acrylic acid along with 400 ml of benzene as solvent and 1.5g of p-toluenesulfonic acid as a catalyst were charged to a resin kettleequipped with a stirrer, condenser, Dean Stark trap, thermometer and gasinlet and outlet. The mixture was heated to reflux and the benzene-waterazeotrope was collected. The amount of water obtained was about 16.0 ml.The reaction mixture was then diluted with 400 ml benzene and washed twotimes with 250 ml portions of 10 percent sodium bicarbonate solution toremove the excess unreacted acid. The thus treated mixture was thenvacuum-stripped to remove the benzene. The mixture was then dried in avacuum oven at 40° C resulting in a solid polyene containing acrylicacid ester group and styrene-allyl alcohol copolymer based polymericbackbone. This solid polyene has an unsaturation of 2.5 mmoles/g and amelting point from about 83°-87° C. This polyene will hereinafter bereferred to as Polyene C.

EXAMPLE 5

To a 1 liter flask maintained under nitrogen atmosphere and equippedwith a stirrer, thermometer condenser and a gas inlet and outlet, wasadded 174 g (1.0 mole) of toluene diisocyanate. To this reaction vessel244 g (1.0 mole) of trimethylol-propane diallyl ether was added at aslow rate to maintain the reactor temperature under 65° C. After theaddition of all the diallyl ether containing alcohol, the reaction wascontinued for 1 hour while maintaining the temperature at about 65° C.The reaction mixture was kept at room temperature overnight. Theresulting product showed an isocyanate (NCO) content of 2.34 meq/g,which indicates that the diallyl ether terminated monourethane wasformed. This product will be referred to herein as ene-isocyanate E.

EXAMPLE 6

A round bottom flask is fitted with a stirrer, thermometer, droppingfunnel, nitrogen inlet and outlet. The flask can be placed in a heatingmantle or immersed in a water bath, as required.

Two moles (448 g) of trimethylol-propane diallyl ether were mixed with0.2 cc of dibutyl tin dilaurate under nitrogen. One mole of tolylene2,4-diisocyanate was added to the mixture, using the rate of additionand cooling water to keep the temperature under 70° C. The mantle wasused to keep the temperature at 70° C. for another hour. Isocyanateanalysis showed the reaction to be essentially complete at this time.The resulting viscous product, an allyl terminated urethane polyenehaving four reactive ene groups, will hereinafter be referred to asliquid Polyene E₂.

The above Polyene E₂ exemplifies a liquid polyene containing at least 2reactive carbon-to-carbon bonds per molecule and having a viscosity inthe range of 0-20 million centipoises at 70° C. The backbone of thesepolyenes is free of reactive carbon-to-carbon unsaturation. This groupof polyenes is illustrated in U.S. Pat. No. 3,661,744. These liquidpolyenes may be added in the subject solid photocurable compositions inamounts ranging from about 0.10 to 15 parts by weight of 100 parts byweight of solid polyene and liquid polythiol.

EXAMPLE 7

110 g of a copolymer of styrene allyl alcohol having an equivalentweight of about 220 and a hydroxyl content of about 7.7 percent andcommercially available from Monsanto Company under the tradename RJ 101,was dissolved in 300 ml of 1,2-dichloroethane in a 1 liter reactionflask maintained under a nitrogen atmosphere and equipped with astirrer, condenser, thermometer and a gas inlet and outlet. 0.16 g ofstannous octoate as a catalyst was added to the reaction flask, followedby dropwise addition over a period of one-half hour of 116 g of theene-isocyanate E prepared in Example 5. The reaction mixture was cooledto room temperature and the solution poured into petroleum ether in anexplosion proof Waring Blender to precipitate a white solid which wasthen filtered and dried. The resulting solid polyene having astyrene-allyl alcohol based polymeric backbone had an unsaturation of3.33 mmoles/g and melted at 60° C. This polyene will hereinafter bereferred to as Polyene D.

CURING PROCESSES EXAMPLE 8

An admixture of 2.0 g of solid Polyene A from Example 2, 0.6 g ofpentaerythritol tetrakis (β-mercaptopropionate), a liquid polythiolcommercially available from Carlisle Chemical Co. under the tradename"Q-43" and 0.15 g of benzophenone was dissolved in 20 g of methyl ethylketone. The solution was spin coated to the copper surface of a cleancopper clad epoxy-glass printed circuit board blank. The methyl ethylketone was allowed to evaporate leaving a 1.0 mil solid photocurablecoating of the admixture on the copper. A negative image-bearingtransparency of a printed circuit was placed in contact with and overthe coating, and the photocurable coating was exposed through thetransparency to UV radiation from 8,000 watt Ascorlux pulsed xenon arclamp at a surface intensity of 4000 microwatts/cm² for about 2 minutes.The major spectral lines of this lamp are all above 3000A. The negativetransparency was removed and the coating was washed in acetone to removethe unexposed, uncured portion thereof, thus exposing the copperthereunder. The imaged circuit board was then etched by spraying it witha ferric chloride solution 42° Baume for about 5 minutes at 50° C toremove the exposed copper, followed by a water wash. The curedphotoresist coating which was not affected by the etching solution wasleft on the etched printed circuit board as a protective cover for thedesired electrical circuit thereunder.

EXAMPLE 9

An admixture of 10.0 g of solid Polyene C from Example 4, 2.5 g of theliquid polythiol "Q-43", 0.12 g of benzophenone and 0.003 g ofphosphorous acid was dissolved in 15 g of chloroform. The solution wascoated onto a about 5 mil thick polyethylene terephthalate i.e. "Mylar"film in a layer of approximately 5 mil thickness by means of a drawbar.After allowing the chloroform to evaporate, a solid non-tackyphotocurable coating of about 2.5 mil was left on the support film.Thereafter the solid photocurable coating on the "Mylar" film wasbrought in contact with a clean copper surface of a circuit boardcomprising a 0.001 inch thick copper cladding on a 0.050 inch epoxyglass substrate. Heat (60° C) and pressure were applied to form thesolid laminate which showed good adhesion to the copper surface. Anegative image bearing transparency of a printed circuit was placed incontact with and over the "Mylar" film and the solid photocurablecoating was exposed through the transparency and UV transparentpolyethylene terephthalate film to UV radiation from a 8000 wattAscorlux pulsed xenon arc lamp at a surface intensity of 4000microwatts/cm² for about 2 minutes. The major spectral lines of thislamp are all above 3000 A. The negative transparency was removed and the"Mylar" film was stripped off. The coating was washed intrichloroethylene to remove the unexposed, uncured portion thereof, thusexposing the copper thereunder. The imaged circuit board was then etchedby spraying it with a ferric chloride solution 42° Baume for about 5minutes at 50° C. to remove the exposed copper, followed by a waterwash. The cured photoresist coating was then removed in methylenechloride solution, thus revealing the desired copper electrical circuit.

The following examples illustrate the use of the subject solidphotocurable compositions as solder-resistant photoresists in themanufacture of printed circuit boards having electrical componentssoldered thereto.

EXAMPLE 10

A photocurable composition was prepared by admixing 952.3 g of1,2-dichloroethane solution containing 389.5 g of the solid polyene A ofExample 2 with 110.5 g of the liquid polythiol "Q-43," 40 g ofbenzophenone, 0.75 g of phosphorus acid, 0.05 g hydroquinone, 0.025 gpyrogallol and 25.0 g of n-butyl phthalate. This photocurablecomposition was coated in a layer of approximately 20 mils by means of adrawbar onto a 2 mil thick transparent polyethylene terephthalate, i.e.,Mylar film which had been placed on a leveled platen heated to 78° C.After drying, a solid photocurable coating of about 8 mils was left onthe Mylar support film. Using a commercial dry film laminating machineequipped with pressure rolls and heated at about 160° F., the surface ofthe Mylar backed dry photocurable coating was laminated onto a cleanedsurface of a conventional double-sided plated through-hole printedcircuit board. Both surfaces of the printed circuit board havetin-solder layers plated over a copper circuit. The circular pad areasof the solder-plated copper circuits have drilled through-holes to allowthe connecting lead of the electrical components to be soldered thereto.The board was placed in a vacuum frame of an exposure unit and anegative transparency of the circuit in which the pad areas are opaqueis registered on the upper surface of the board. The solid photocurablecoating was exposed through the transparency to UV radiation from an8000 watt Ascorlux pulsed xenon arc lamp at a surface intensity of 3000microwatts/cm² for about 6 minutes, thereby curing the photocurablesolder resist composition in all areas except those corresponding to thepads having the through-holes. Following the exposure, the negative isremoved and the Mylar support film is stripped off. The unexposed,uncured solder resist composition was washed off the circuit board, thusbearing the unexposed tinsolder plated pad areas of the circuit. Thisdevelopment was carried out in a commercial spray developer for 45seconds using a solvent containing a mixture of 1,2-dichloroethane and10 percent by volume of an alkylated aryl polyether alcohol surfactantcommercially available from Rohm & Haas Co. under the tradename TrisonX-100. Thereafter the circuit board was given a thorough water rinsefollowed by a drying treatment in two successive high velocity forcedair ovens. The circuit board was dried at 65° C for 1 hour in the firstoven and at 90 ° C for one-half hour in the second oven.

The photocured resist protected printed circuit board was then submittedto a soldering treatment in a commercial wave soldering apparatus. Theleads of the electrical components are inserted through the pads in thecircuit board, and the board was passed over a foaming flux, i.e.,"Milfoam-613 Flux," a rosin based isopropyl alcohol containing fluxcommercially available from Alphametals Inc., Jersey City, New Jersey,to coat the areas to be soldered with flux. The board was then conveyedover a preheater which preheated the circuit board to a temperature ofabout 210° F and then over a solder bath containing 63/37 tin-lead alloymaintained at 500° F. The solder contacts the underside of the board,thereby soldering all the contact leads extending therethrough to thecircuit board. After washing the board with the soldered components in asuitable solvent such as 1,1,1-trichloroethane or ethylene dichloride toremove residual flux and solder oil, the board was then dried.Inspection of the board showed that the cured solder resist compositionwithstood the soldering environment and adhered well to the board.

EXAMPLE 11

Example 10 was repeated except that the aforementioned photocurablecomposition contained 12.0 g of n-butyl phthalate and 25.0 g of liquidPolyene E₂ from Example 6 and prior to submitting the circuit board tothe soldering treatment the developed board was first dried in a 75° Coven for 1 hour and then in a 95° C oven for 1/2 hour. Inspection of theboard showed that the electrical components were securely soldered tothe circuit board and that the cured solder resist composition wasunaffected by the soldering steps and adhered well to the board.

EXAMPLE 12

A photocurable composition was prepared by admixing 400 g of a1,2-dichloroethane solution of the solid Polyene D in Example 7 (as 46weight percent solids) with 41.0 g of "Q-43, " 18 g of benzophenone,0.68 g hydroquinone, 1.0 g pyrogallol and 0.88 g phosphorous acid. A drysolid photocurable layer of about 6 mils was formed on a Myler supportfilm using the coating techniques described in Example 10. The surfaceof this supported photocurable layer was laminated to the surface of aplated through-hole printed circuit board, exposed, and developed in themanner outlined in Example 10, except that the length of exposure to UVradiation was 4 minutes, development of the exposed layer to wash offthe uncured photocurable layer was 1 minute, and the drying treatmentwas carried out first in a 75° C oven for 15 minutes and then in an 90°C oven for 45 minutes.

The photocured resist protected printed circuit board was subjected to asoldering treatment described in Example 10. Inspection of the boardshowed that the electrical components were securely soldered to thecircuit board and that the cured solder resist composition withstood thesoldering environment and adhered well to the board.

It is noted in the above examples only one surface of the double sidedprinted circuit board was coated with the subject solder resistantphotoresist compositions. If desired, the coating with solder resistlayer, exposure and development steps can be repeated on the othersurface of the printed circuit board. Similarly, the subject solderresistant photoresists can be utilized in soldering operations employingsingle sided printed circuit boards.

The molecular weight of the polyenes and polythiols of the presentinvention, as well as the starting styrene-allyl alcohol copolymermaterials of this invention, may be measured by various conventionalmethods including solution viscosity, osmotic pressure and gelpermeation chromatography. Additionally, the molecular weight may becalculated from the known molecular weight of the reactants.

As can be seen from the above detailed description, the subject solidcurable and particularly photocurable compositions comprised ofcompatible solid polyenes and solid polythiols having similar polymericbackbones based on styrene-allyl alcohol copolymers exhibit extremelysatisfactory chemical and physical properties and are versatile curablepolymeric systems which do not possess the many drawbacks of liquidcurable polymer compositions.

A desirable characteristic of these solid photocurable polyene-polythiolcompositions is that solid films of the same may be formed easily byknown film forming techniques and the solid photosensitive film can bepackaged as a sandwich between removable protective cover sheets such aspolyolefin films and a flexible, usually UV transparent, supportpolymeric film composed of polyesters, cellulose esters, polyamides,etc. In this manner they can be easily stored and handled and when readyfor use can be directly laminated, usually under pressure and heat, tothe desired solid surface, e.g., metal clad printed circuit board. Thesolid uncured polyene-polythiol composition adheres very satisfactorilyto various surfaces, particularly to copper.

It is understood that the foregoing detailed description is given merelyby way of illustration and that many variations may be made thereinwithout departing from the spirit of this invention.

What is claimed is:
 1. A solid curable composition useful for obtaining a solid cross-linked polythioether consisting essentially of:1. a solid polyene which is the reaction product of a styrene-allyl alcohol copolymer and at least one reactive unsaturated monocarboxylic acid, said polyene containing at least 2 reactive carbon-to-carbon bonds per molecule; and
 2. a liquid polythiol containing at least 2 thiol groups per molecule, the total combined functionality of (a) the reactive unsaturated carbon-to-carbon bonds per molecule in the polyene and (b) the thiol groups per molecule in the polythiol being greater than
 4. 2. The composition of claim 1 wherein (1) said polyene has the general formula: ##STR13## wherein Q is a styrene-allyl alcohol copolymeric moiety remaining after n hydroxyl groups of a styrene-allyl alcohol copolymer have reacted to form n ester linkages in the formula; A and B are polyvalent organic radical members free of reactive carbon-to-carbon unsaturation and are independently selected from the group consisting of aryl, substituted aryl, aralkyl, substituted aralkyl, cycloalkyl, substituted cycloalkyl, alkyl and substituted alkyl containing 1 to 36 carbon atoms and mixtures thereof, said group members can be internally connected to one another by a chemically compatible linkage selected from the group consisting of --O--, --S--, carboxylate, carbonate, carbonyl, urethane and substituted urethane, urea and substituted urea, amide and substituted amide, amine and substituted amine and hydrocarbon; Z is a divalent chemically compatible linkage selected from the group consisting of ##STR14## --O-- and --S--; X is a member selected from the group consisting of (a) --(CH₂)_(d) CR'=CHR, (b) --O--(CH₂)_(d) --CR'=CHR, (c) --S--(CH₂)_(d) --CR'=CHR, (d) --(CH₂)_(d) --C═CR, (e) --O--(CH₂)_(d) --C|CR, (f) --S--(CH₂)_(d) --C|CR; and mixtures thereof; where R and R' each are independently selected from the group consisting of hydrogen and methyl radicals; d, k, p and q are each integers from 0 to 1; y is an integer from 1 to 10; m and n are each integers of at least 1; with the proviso that when n is 1, y or m is at least 2; and (2) said liquid polythiol has a molecular weight in the range about 94 to 20,000 and is of the general formula: R₈ --(SH)_(x) wherein x is an integer of at least 2 and R₈ is a polyvalent organic radical member free of reactive carbon-to-carbon unsaturation.
 3. The composition of claim 2 wherein said polyene has the formula: ##STR15## wherein y is an integer from 1 to 5; A and B are polyvalent radical members independently selected from the group consisting of phenyl, benzyl, alkyl, cycloalkyl, substituted phenyl, substituted benzyl, substituted alkyl and substituted cycloalkyl, said substituents on said substituted members selected from the group consisting of nitro, chloro, bromo, acetoxy, acetamido, phenyl, benzyl, alkyl, alkoxy and cycloalkyl; said alkyl and alkoxy having 1 to 9 carbon atoms and said cycloalkyl having from 3 to 8 carbon atoms.
 4. The composition of claim 2 wherein said polyene has the formula: ##STR16## wherein R₄ is a monovalent radical member selected from the group consisting of hydrogen, methyl, ethyl, --O--(CH₂)_(d) --CH=CH₂ and --O--CH₂ --C--[CH₂ --O--(CH₂)_(d) --CH=CH₂ ]₃ ; and m is an integer from 1 to
 4. 5. A composition of claim 1 wherein (1) said polyene is a reaction product of a styrene-allyl alcohol copolymer and at least one reactive unsaturated monocarboxylic acid selected from the group consisting of acrylic acid, methacrylic acid and vinyl acetic acid; and styrene-allyl alcohol copolymer reactant having an equivalent weight of about 300± 130 and a hydroxyl group content from about 4 to 10 percent by weight; and (2) said polythiol is an ester of a polyhydric alcohol containing at least 2 hydroxyl groups per molecule and at least one mercaptocarboxylic acid selected from the group consisting of mercaptoacetic acid, α-mercaptopropionic acid and β-mercaptopropionic acid.
 6. The composition of claim 1 wherein said styrene-allyl alcohol copolymer reactant has a hydroxy group content from about 1.8 to 10 percent by weight and a styrene content from about 30 to 94 percent by weight.
 7. An article comprising the cured composition of claim 1 as a coating on a substrate.
 8. An article comprising the cured composition of claim 1 as an adhesive between two substrates.
 9. A shaped, molded article from the cured composition of claim
 1. 